The bug

If the game was launched in demo mode, exiting the demo world causes the game to indefinitely show the "saving world" fullscreen message.

This issue is be encountered when the Save and Quit to Title button is clicked on the pause menu, or when the Minecraft window is closed while the world is being played (in which case it hangs on a black screen with no content). Note that saving of the demo world doesn't seem to be affected, so the world still saves correctly without data loss.

Steps to reproduce

1. Launch the game in demo mode. This can be done by signing into the Minecraft Launcher with an account that doesn't own Minecraft (untested), or with the Launch Demo button in Prism Launcher.
2. Click the Play Demo World button to enter the demo world
3. Open the pause menu with Esc
4. Press the save and quit button

Observed behavior

The saving world screen is shown, but the game never returns to the main menu. When in this state, the background panorama continues to spin but no further attempts to quit the game are responded to.

Expected behavior

The saving world screen is shown for a brief period of time, and then the main menu is shown.

Notes

• I have not experienced this issue when running the game in non-demo mode, and it has been consistently happening for a while in demo mode. Therefore, I doubt that this is simply a fluke storage read/write error or similar.

Workaround

As a workaround to this issue, you can force the game to close by "killing" its process. This can be done under Linux with the xkill program or a similar feature provided by your desktop environment. Some third-party launchers also provide a button to easily kill Minecraft, e.g. Prism Launcher.

Note that to ensure the world can save properly, you should wait a few seconds before killing Minecraft's process.

Screenshots

The "saving world" fullscreen message

The black screen shown if Minecraft is closed while in-game